How To Calculate Safe Period To Avoid Pregnancy?

How To Calculate Safe Period To Avoid Pregnancy?

Medically Reviewed By
Dr. Prerna More Patel (Gynecologist/Obstetrician)
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For thousands of years, people have been determining infertile days or safe periods for intercourse to avoid pregnancy. Once you understand the menstrual cycle and what happens in each phase, you can calculate safe days more accurately. The significance of infertile days is relevant to ensuring a safe and responsible approach to sexual intimacy, empowering individuals with the knowledge to make informed decisions about contraception. In such situations, a period calculator is invaluable for understanding your menstrual cycle and identifying safe sex periods. The premise behind a safe period calculator is to prevent an unwanted pregnancy naturally, without any side effects. This article will help you discover the art of timing and knowledge to navigate a safe period and prevent unplanned pregnancy.

What is a Safe Period (Unfertile Period)?

As a woman grows older, her menstrual cycle often changes. A normal cycle lasts between 24 to 38 days. ‘Safe period’ refers to the days when a woman has reduced chances of getting pregnant. So, if you do not want a baby and do not want to use contraceptives either, this is the time you should have sex with your partner.

Biologically speaking, this is the time when the egg is not present to be fertilised.  If you have intercourse with no egg, you cannot get pregnant because this is the unfertile period in a menstrual cycle.

For most women, ovulation occurs approximately 14 days before the next menstrual cycle starts. It isn’t easy to know exactly when you will start your next menstrual cycle. However, if your periods are mostly regular, it is easy to calculate ovulation days. To do this, you need to use the date of the previous menstrual cycle as a starting point. It is important to note that an egg can be fertilised only four days before and three days after ovulation. In other words, this is not a safe period, so you should avoid intercourse.

Why Should You Calculate Your Safe Period?

Calculating your safe period is advantageous because it will help you understand what days it is favourable to have sex without protection and with no pregnancy scares. Knowing how to calculate your safe period is essential if you do not wish to have a child right away. However, more importantly, safe period calculation is a great method of birth control because it does not involve ingesting hormonal birth control pills, using an IUD, or hormone injections which can have different effects on different women, ranging from extreme mood swings to weight gain and other problems that hamper one’s well-being.


How to Calculate Your Safe Period to Avoid Pregnancy?

To calculate your safe days, you need to understand the various phases of the menstrual cycle.

Phases of the Cycle

The menstrual cycle can be divided into three phases: the follicular phase (pre-ovulation phase), the ovulation phase, and the luteal phase (post-ovulation phase). The duration of each phase varies from woman to woman. However, the average menstrual cycle is believed to be 28 days. The menstrual cycle is counted from the first day of menstrual bleeding. Let’s look at what happens in each phase.

1. The Follicular Phase / Proliferative Phase

The follicular phase occurs before ovulation. In this phase, the maturation of the follicles in the ovary takes place. This phase ends with ovulation. In this stage, estradiol is the hormone at work, and the Follicle-Stimulating Hormone (FSH) is secreted.

2. The Ovulation Phase

It is in the ovulation phase that a mature ovarian follicle ruptures and discharges an ovum (also known as an egg). The time just before and after ovulation is usually referred to as the ovulation phase. A woman could get pregnant on the days she is ovulating.

3. The Luteal Phase / Secretory Phase

The luteal phase is the last phase of the menstrual cycle. It is marked by the creation of the corpus luteum and terminates in either pregnancy or degradation of the corpus luteum. The corpus luteum is a temporary endocrine structure that helps produce oestrogen and progestogen. The body needs oestrogen and progestogen to maintain the endometrium, the inner lining of the uterus.

The safe days for a woman after a period depend on the lifespan of both the sperm and egg. In most cases, ovulation happens on the 14th day of the menstrual cycle if the menstrual cycle is of average length (28 days). The ovulation time varies for each woman and can occur from the 12th day to the 19th day of the cycle. A sperm usually lives for 3 to 5 days in the reproductive tract. Therefore, it is possible to become pregnant  unprotected sex is had five days before ovulation. The lifespan of the egg is quite short- only about 24 hours. If fertilisation does not occur within that time frame, the egg will die.

How to Calculate Your Safe Period to Avoid Pregnancy?

Safe Period Chart to Avoid Pregnancy

Here is a quick look at the breakup of safe days and unsafe days which simplifies the calculation for you and explains how to count your safe days:

Safe times using the calendar method
Sunday Monday Tuesday Wednesday Thursday Friday Saturday  
Start of period 1 2 3 4 5 6 7 Safe Days
8 9 10 11 12 13 14 Unsafe days
15 16 17 18 19 20 21 Unsafe Days
22 23 24 25 26 27 28 Safe Days
Start of period 29 30 1 2 3 4 5 Safe Days

When to Have Sex to Avoid Pregnancy?

1. What Is a Safe Period to Have Sex?

A thumb rule – If you are having sex, you can get pregnant! Despite all calculations and theories, there is no definite way to determine when a woman will ovulate, so many factors come into play. Most women ovulate 12 to 14 days before their period, but some ovulate at a different time. So, figuring out when it is safe to have sex yet avoid pregnancy is quite a guessing game.

2. How Long Is a Safe Period?

Based on their experiences, many women believe it is safe to have sex and avoid getting pregnant just after their period starts or before it begins. Beware, fluctuating hormones and changing schedules can make these calculations inaccurate. As a general rule, if your cycle is a regular one (28 days), the seven days before your period should be the safe period. But do not forget that this calculation works only if your periods are regular. Here’s what a missed period may mean.

3. How to Calculate the Time of Ovulation?

Safe period and ovulation are related because safe days are calculated based on ovulation. According to the popular Safe Period Calculator method, days 1 to day 7 are safe and unfertile in a regular menstrual cycle which lasts  26 to 32 days. This considers the premise that the lifespan of the sperm in the reproductive canal is 3 to 5 days. This method calculates that ovulation occurs on the 19th day. Therefore, fertilisation can occur until the 20th day of the cycle. Since all these calculations are approximated, the results can vary from woman to woman.

This calculation is adjusted to reflect WHO (World Health Organization) data that shows that approximately 80% of menstrual cycles range between 26 to 32 days.

Different Methods to Calculate Safe Period

Here are some methods you can use to calculate  your safe period:

Safe Period Calculator or Menstrual Cycle Calculator

Cycle calculators are accurate in most cases. However, many people find these calculators and apps very complex. Also, most of the information they ask to calculate the infertile period – for example, months of data about body temperature, cervical mucus and dates of menstruation – may not be readily available to every woman. Put, to use these calculators, you would need data about your periods as well as body temperature handy. Therefore, many prefer using simpler period calculators like the ones below, which do not ask for months of data but still give accurate results.

1. Avoid Your Fertile Days

Avoid your fertile period. Remember, safe days depend on different cycle lengths. The following table lists the most fertile days for various cycle lengths. If you do not want to get pregnant, you need to avoid intercourse on the following days:

Length of Cycle Most Fertile Days
24 days Days 5 to 10 of the cycle
28 days Days 9 to 14 of the cycle
30 days Days 11 to 16 of the cycle
35 days Days 16 to 21 of the cycle

2. Calculate When You Are Less Likely to Get Pregnant

Keeping track of your periods for at least six months will help map your fertile days.

Step 1:

Use this formula: Subtract 18 days from the total days of your shortest cycle. Using the resulting number, count from the first day of your next period and mark that date on your calendar.

Step 2:

Subtract 11 days from your longest cycle. Using that number, count forward from the first day of your next period. Mark that date on the calendar.

Step 3:

Your most fertile period is between those marked dates. It should be safe to have unprotected sex other than on those dates. However, bear in mind that sperm live up to 4 days so counting four days on either side is risky too. Note that this only works if your periods are regular.

3. Who Can Use the Safe Period Calculator?

You need to ask your doctor about the efficiency of natural family planning methods. The doctor will do a check-up and let you know if these would be effective for you. Use the safe period calculator as a natural birth control method only after your doctor gives the go-ahead.

Suppose your menstrual cycle is regular and falls in the average range of 26 to 32 days, and the variation between your longest and shortest cycles is about seven days. In that case, you should be safe using the safe period calculator method as birth control.

4. Who Cannot Use the Safe Period Calculator?

Applying the same rule as above–if you are in the regular 26-day to 32-day cycle and the variation between your longest and your shortest cycle is more than eight days, then it would be risky to use this method.

Do remember that because of hormonal changes, it would be wiser to wait for six months after childbirth to use this method.

Also, because of erratic cycles, this method is unsuitable for teenagers or women in menopause. This method might not work for women with erratic cycles because of conditions like PCOS and hormonal imbalance.

5. Examples of Calculating Safe Periods

Calculating a safe period can be confusing. Here are two examples of calculating the same.

  • Take the example of a woman who has 24 days between 2 menstruating cycles. This means that her ovulation would be ten days after the first day of her last period. Based on this (24 minus 14) calculation, her safe period would be from day one to day six after her last period and from day thirteen to her next period.
  • Let’s take another example of a woman with 32 days between 2 menstruation cycles. Her ovulation would be 18 days after her last period. Based on this calculation (32 minus 14), her safe period would be from day one after the last period to day 14 and from day 21 to the next period.
  • Safety: Women with regular menstruating cycles have an 85% safety ratio for not getting pregnant in 12 months. However, the success rate depends on how well you calculate the safe period and how religiously you follow it.
  • Handy Technology: In today’s world of technological advancement, numerous apps can help you chart your menstrual cycle, calculate your infertile days and store all this data for your quick reference!

Calculating Safe Periods

  • Many tools, like a menstrual cycle calculator, are available. These tools will give you a rough estimate of your ovulation period. As a result, you can calculate ovulation and the safe period with higher accuracy and greater ease.

Natural Family Planning (Fertility Awareness-based Methods)

Basal body temperature is the lowest non-pathologic, natural temperature recorded after rest.  Your body demonstrates various signs in the ovulation phase. If you recognise these signs and avoid sex when you see these signs, you can avoid pregnancy. This is also called natural family planning.

Various fertility awareness-based methods are:

1. Basal Body Temperature Method

Charting your basal body temperature is quite easy. To put it simply, what you do is take your temperature first thing every morning and plot it on a chart.

  • Some women experience a drop in body temperature when they are ovulating.
  • If you see a temperature shift lasting at least three days or occurring at the end of your cycle, you can draw a line between your follicular phase and luteal phase temperature. You might also observe a clear shift and be able to track the path between the lowest luteal phase BBT and the highest follicular phase BBT.
  • Analyse the chart at the end of the month to find the pattern.
  • Create a chart for 3-6 months to see a clear pattern.
  • If your temperature does not decrease for more than 18 days, we recommend you do a pregnancy test at home or see a doctor.

2. Charting Basal Body Temperature

Keep these 4 rules in mind  when charting your basal body temperature:

  • First 5 days rule: For the most part, you can assume that you are infertile during the first five days of your menstrual cycle. This may not be accurate if you have had a cycle that was shorter than 25 days. To determine this, track your menstrual cycle for about six months.
  • Dry day rule: You might be infertile when you don’t observe any cervical fluid.
  • Peak plus 4 rule: Your infertile period starts on the 4th evening after your most fertile cervical fluid (CF). This is when your CF becomes infertile again, and there is a clear BBT shift.
  • Temp plus 3 rule: You might be infertile on the evening of the 3rd day after your BBT shift.

Safe Period calculation

Women with regular menstruating cycles have an 85% safety ratio for not getting pregnant. However, the success rate depends on how well you calculate the safe period and how religiously you follow it.

Once you figure out how to track the signs of fertility, you can safely indulge in unprotected sex during the infertile period. If you think you are at risk of being fertile, use protection or abstain.

It is important to remember that no method is foolproof. While most methods are accurate and time-tested, hormonal ups and downs in a woman’s body can make your calculations go awry. It’s best to follow the golden rule: assume you’re fertile when in doubt.

3. Cervical Mucus / Ovulation Method

The colour of cervical mucus changes when you are ovulating. Note the colour of cervical mucus every day. A colour change would indicate that you are in the ovulation phase.

Here is how you can interpret your cervical mucus:

  • The flow masks the mucus during menstruation.
  • No mucus is produced for a few days after menstruation. These ‘dry days’ are safe.
  • When the ovum ripens for the next cycle, mucus production increases. It appears yellow, white, or cloudy and feels sticky.
  • Clear, slippery mucus, which is stretchable, indicates the most fertile days of the cycle.
  • A few ‘dry days’ after clear mucus indicates the onset of the next period.

4. Sympto-thermal Method

A combination of multiple methods involves tracking ovulation symptoms like pain in the abdomen, heaviness and tender breasts, body temperature, and mucus colour. Using different methods simultaneously ensures that the safe days are predicted more accurately.

5. Cycle Beads App

The Cyc leBeads smartphone app is available for both Android and iPhone users. It is based on the same name’s highly effective family planning method.

  • Enter the start date of your most recent period.
  • The screen will show you where you are in your menstrual cycle and the chances of pregnancy on that day.
  • This method is most effective for women with a menstrual cycle from 26 days to 32 days.
  • Women with a cycle falling outside this range should use a different method of family planning.

Here is how to use the cycle beads:

  • Place a rubber ring in the red bead on the first day of the period.
  • Move the band over the beads in the direction of the arrow.
  • The brown beads indicate safe days. The white beads indicate unsafe days.

6. Standard Days Method

Similar to the calendar method, this method involves tracking your cycle for eight to ten continuous cycles and is effective only if your cycle is more than 27 days.

Here is how you can predict safe days using this method:

  • Consider the shortest cycle for the calculation of the first fertile day.
  • Subtract 18 from the total number of days.
  • Use the result to count from the first day of your cycle to mark the first fertile day.
  • Consider the longest cycle for the calculation of the last fertile day.
  • Subtract 11 from the total number of days.
  • Use the result to count from the first day of your cycle to mark the last fertile day.

When you have identified your first and last fertile days, it is easy to track the safe sex days too.

Standard assumptions:

  • Sperm lives for 4-6 days in the reproductive tract and can fertilise an egg during this period.
  • Only one egg is released per cycle and lives for 24 hours, during which time it can be fertilised.
  • The most fertile period is 7 days before ovulation and 3-4 days after your period.

How Effective Are Fertility Awareness Methods (FAMs) to Avoid Pregnancy?

Because of many variable factors, the safe-days method is not 100% reliable. Some women trust this method completely. Hormonal changes (that you are not aware of) and irregular periods can cause errors in calculating the infertile period. Condoms are the easiest option, but if you dislike using them, then the next best choice is oral contraception.

FAMs will work only if:

  • You are meticulous with the safe period calculation and follow it accurately.
  • Your partner is willing to follow the safe-days-only sex method.
  • You use other forms of contraception on your fertile days.

What Are the Advantages of Using Fertility Awareness Methods to Avoid Pregnancy?

If used correctly, FAMs can give you reasonable protection from unwanted pregnancy.

Some advantages of using FAMs are:

  • No expense
  • No medication, therefore no side effects.
  • Greater understanding between a couple.
  • Some religious beliefs do not allow artificial contraception, so the safe day’s method is preferred.
  • By opting for fertility awareness methods, individuals contribute to a sustainable approach to contraception, reducing the environmental impact associated with the production, packaging, and disposal of traditional contraceptives.
  • Fertility awareness methods foster a deeper connection with one’s body, promoting self-awareness and empowerment as individuals better understand their unique reproductive cycles.

What Are the Disadvantages of Using Fertility Awareness Methods to Avoid Pregnancy?

  • Difficult to implement if your partner is unwilling to follow this method.
  • No protection against sexually transmitted diseases.
  • Some medicines (even over-the-counter ones) can cause errors in calculation.
  • Sometimes the tracking of periods becomes cumbersome, and calculations can be inaccurate because of hormonal changes.
  • Tracking and calculating fertility cycles can sometimes add stress and anxiety to individuals or couples relying solely on fertility awareness methods for contraception. 
  • Fertility awareness methods require careful planning and adherence to specific windows of fertility and infertility. This can limit the spontaneity and freedom of engaging in sexual activity.

Things to Remember About Having Sex During the Safe Period

  • First and foremost, there is no such thing as a 100% safe period.
  • It works best if your periods are regular because fluctuating cycles can cause an aberration.
  • If your menstrual cycle days fluctuate by more than eight days in a six-month period, the safe day calculation will not work.
  • Sometimes you might need to use emergency contraceptive pills to avoid a pregnancy.

Other Ways to Have Sex Without Worrying About Getting Pregnant

Looking for other ways to have sex without worrying about conception? We’ve got you covered.

1. Use a Condom

The easiest method of contraception, condoms also protect you from STDs.

2. Try New Positions, Places and Tricks

Spice up things by having intercourse in different positions and places in the house!

3. Invest in Sex Toys

With couples shedding their inhibitions in the bedroom, it is easy to find a sex toy which you both love. Choose from vibrators, dildos and more for a pleasurable experience.

4. Sexy Foreplay

Engage in a game of strip poker or invent a game of your own to add fun to foreplay.

The FAM is one birth control method, but it has disadvantages. So, ensure you are vigilant and thorough with your calculations to avoid an accidental pregnancy.


1. Can You Have Sex While on Period?

Yes, it is possible to have sex while on your period. However, some individuals may find it messy or uncomfortable. It’s important to note that even during menstruation, there is still a slight risk of pregnancy, especially if you have a shorter menstrual cycle.

2. How Many Days After My Period Will I Ovulate?

If your cycle is regular, ovulation happens 14 days before your subsequent period. If you have a healthy reproductive system and a typical 28-day menstrual cycle, you will ovulation around the 14th day. You may ovulate at any moment between the eighth and nineteenth day in a cycle that lasts between 26 and 32 days.

3. Can I Get Pregnant If Having Sex Immediately After My Period?

While the chances of getting pregnant immediately after your period are relatively low, it is still possible. Sperm can survive in the female reproductive tract for up to 5 days. If you have a shorter menstrual cycle, you will likely ovulate shortly after your period ends. Therefore, it’s important to use contraception consistently to avoid pregnancy.

4. When a Woman Can’t Get Pregnant?

Various factors can contribute to a woman’s inability to conceive, such as underlying medical conditions, hormonal imbalances, age-related factors, or issues with the reproductive organs. If a woman has been actively trying to conceive without success for a prolonged period (typically one year), it is recommended to consult a healthcare professional for a comprehensive evaluation.

5. How Many Days Are You Safe in a Month?

The length of periods and the ovulation date, which are subject to alter due to several circumstances, determine the safe sex period within each month. Therefore, any period extending past the fertile window may be considered safe, but not fully, as pregnancy risks still exist.

6. Is There a Health Risk of Unprotected Sex During the Safe Period?

Unprotected intercourse poses hazards for the development of unintended pregnancy, STDs, and other infections (such as UTIs), necessitating contraceptives at any time of the month.

7. What to Do When You Become Pregnant During the Safe Period?

It may be unexpected but not impossible if you become pregnant during the safe period or while using fertility awareness methods. It is advisable to consult a healthcare professional to confirm the pregnancy and discuss your options, whether it is continuing the pregnancy or considering other alternatives. They can provide guidance and support throughout the decision-making process.


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2. Your menstrual cycle; OASH;

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4. Physiology, Ovulation And Basal Body Temperature; NIH;

5. Su. HW, Yi. YC, Wei. TY, et al.; Detection of ovulation, a review of currently available methods; PubMed Central;; September 2017

6. LACTATIONAL AMENORRHEA AND OTHER FERTILITY AWARENESS BASED METHODS; Health Maryland;,Contraception,LAMandNaturalFamilyPlanning,Final,2012.pdf?Mobile=1&&Source=/mch/_layouts/mobile/dispform.aspx?List=f396a900%2D4316%2D484d%2Dacb0%2Ddaaa3ea27815&&View=fc60c706%2D8e28%2D4618%2D8efa%2D9e39bf027ec3&&ID=786&&CurrentPage=1

7. Can I get pregnant just after my period has finished?; NHS;

8. Anzillote. AW; When’s the Best Time to Have Sex and Avoid Pregnancy?; Nemours Teens Health;

Also Read:

Calendar Based Methods of Contraception
Can You Get Pregnant on Your Period?
Calendar Method of Family Planning

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